1. Field of the Invention
The present invention relates to batteries including pressure-sensitive current-interruption structures. In particular, the present invention relates to a battery including a pressure-sensitive current-interruption structure preferably used for a lithium-polymer secondary battery.
2. Description of the Related Art
Hitherto, reduction in size and thickness has been required of devices such as mobile phones and camcorders. Accordingly, batteries used in these devices have also been required to be reduced in size and to have a low profile. A lithium-polymer secondary battery may be selected as a likely candidate to meet these requirements.
Even when a battery is made smaller, measures for safety must be taken. When a lithium-polymer secondary battery is overcharged or is charged by an electrical current larger than a specified value, chemical reactions occur in the lithium-polymer secondary battery, thereby producing gas and increasing pressure in the battery. Therefore, there is a risk of cracks forming in the casing of the lithium-polymer secondary battery and the explosion thereof.
Therefore, pressure-sensitive current-interruption structures have been proposed which cut electrical paths between power-generating units and external terminals of batteries when the internal pressure of the batteries increases above predetermined values.
A pressure-sensitive current-interruption structure is disclosed in, for example, U.S. Pat. No. 4,943,497, in which an explosion proof valve, which expands toward the outside as the pressure in a battery rises, is provided in a metallic case of the battery, and the metallic case is separated from an internal electrode when the explosion proof valve expands toward the outside due to the pressure rise, thereby interrupting electrical current.
A plate-shaped lithium-polymer secondary battery which is now widely used is covered by an outer cover formed by laminated films and the battery body has a thickness of only 1 to 4 mm. Therefore, there is a problem in the known lithium-polymer secondary battery in that spaces for receiving a diaphragm cannot be secured, the diaphragm cannot be affixed, and it is difficult to mount the diaphragm when the diaphragm, etc., are mounted on an end face of a metallic case of the battery.
On the other hand, when a diaphragm or an interruption structure using the same is mounted on a plate-shaped surface (a major surface) of the battery, the thickness of the thin plate-shaped battery is increased.
Accordingly, it is an object of the present invention to provide a battery including a pressure-sensitive current-interruption structure which can be mounted without increasing the size and the thickness of the battery by using a space formed in a sealed part of a casing. The pressure-sensitive current-interruption structure can be positioned accurately and be affixed easily compared with a method in which an interruption structure is bonded to a sealed part of a casing. The pressure-sensitive current-interruption structure is not affected by an adhesive or the like and is not significantly affected by the strength of the sealed part of a casing.
To these ends, according to an aspect of the present invention, a battery including a pressure-sensitive current-interruption structure comprises a plate-shaped power-generating unit; a casing hermetically sealed and containing the power generating unit, deformable by an internal pressure; a plurality of lead terminals which are electrical paths from the power generating unit to the outside of the casing; a sealed part, which is a part of the casing, disposed at an end of the power generating unit and formed thinner than the thickness of a space receiving the power generating unit; and an interruption structure. The interruption structure includes an operating member disposed outside the casing, at least one end of the operating member being disposed above or under the power generating unit and displaceable toward the outside as the internal pressure rises; a fixing member having at least one part thereof being positioned opposing the operating member across the power generating unit; an insulative holding member disposed above or under the sealed part of the casing and fixed to the fixing member; and an element having an electrically conductive path, held by the holding member, the element being electrically connected to at least one of the lead terminals at one end of the element and to an external electrode at the other end of the element. The other end of the operating member is positioned at the sealed part side of the element, the other end of the operating member being displaced in accordance with the displacement of the one end of the operating member caused by the internal pressure, thereby cutting the element when displacing over a predetermined value. With this arrangement, the battery can be made compact and the thickness thereof is not increased by using a space formed at the sealed part of the casing. Therefore, compared with a method in which an interruption structure is bonded to the sealed part, the interruption structure can be affixed easily by being positioned accurately without being affected by an adhesive (for example, by variation in adhesive strength due to temperature variation, elapse of time, a gas, variation in the thickness of the adhesive, and the like), and the strength of the sealed part (top seal) does not significantly affect the characteristics of the interruption structure.
According to another aspect of the present invention, a battery including a pressure-sensitive current-interruption structure comprises a plate-shaped power-generating unit; a casing hermetically sealed and containing the power generating unit, deformable by an internal pressure; a plurality of lead terminals which are electrical paths from the power generating unit to the outside of the casing; a sealed part, which is a part of the casing, disposed at an end of the power generating unit and formed thinner than the thickness of a space receiving the power generating unit; and an interruption structure. The interruption structure includes an insulative holding member disposed above or under the sealed part of the casing and fixed to a fixing member; an element having an electrically conductive path, held by the holding member, the element being electrically connected to at least one of the lead terminals at one end of the element and to an external electrode at the other end of the element; and an operating member disposed outside the casing, one end of the operating member being disposed above or under the power generating unit and displaceable toward the outside as the internal pressure rises, the other end of the operating member being disposed in the vicinity of the element. The other end of the operating member is positioned opposite to the one end with respect to a supported part of the operating member and opposite to the sealed-part of the casing with respect to the element, the other end of the operating member being displaced in accordance with the displacement of the one end of the operating member in the opposite direction caused by the internal pressure, thereby cutting the element when displacing over a predetermined value. With this arrangement, the operational pressure can be stable.
The operating member and the fixing member are preferably connected to each other. With this arrangement, the element is not likely to be damaged while handling during transportation and the like. When the operating member and the fixing member are not connected to each other, a laborious work, such that the operating member is tentatively affixed by a tentatively affixing material and the affixing material is removed after mounting, is necessary.
The operating member and the fixing member may be formed integrally with each other. With this arrangement, the number of components can be reduced, manufacturing processes can be simplified, and the components can be positioned accurately.
The operating member may include a contact part for receiving an external force applied to a surface of the operating member, and the fixing member may include a supporting platform to come into contact with the contact part. With this arrangement, the element is not likely to be damaged when an external force is applied to the operating member in a direction perpendicular to the surface thereof.
A fixing part between the fixing member and the holding member may be positioned at the same level as that of the operating member. With this arrangement, a wide freedom in designing is provided. That is, when the holding member holds the operating member and the fixing member at the level of the fixing member, the relationship of positions between the operating member and the holding member varies according to the thickness of the battery or the sealed part of the casing, whereby the relationship of positions, the strength of each component, and the like must be redesigned in accordance with the variation in size or the like of the components. When the operating member and the fixing member are held by the holding member at the level of the operating member, only the distance between the operating member and the fixing member must be changed, and complex redesigning is not necessary.